Embodiments of the present application relate generally to optical networking hardware, and more particularly to a system and method for performing on-chip bit error rate (BER) testing on a physical layer multimode device.
High-speed digital communication networks over copper and optical fiber are used in many network communication and digital storage applications. Ethernet and Fiber Channel are two widely used communication protocols, which continue to evolve in response to increasing need for higher bandwidth in digital communication systems. The Open Systems Interconnection (OSI) model (ISO standard) was developed to establish standardization for linking heterogeneous computer and communication systems. It describes the flow of information from a software application of a first computer system to a software application of a second computer system through a network medium.
The OSI model has seven distinct functional layers including Layer 7: an application layer; Layer 6: a presentation layer; Layer 5: a session layer; Layer 4: a transport layer; Layer 3: a network layer; Layer 2: a data link layer; and Layer 1: a physical layer. Importantly, each OSI layer describes certain tasks which are necessary for facilitating the transfer of information through interfacing layers and ultimately through the network. Notwithstanding, the OSI model does not describe any particular implementation of the various layers.
OSI layers 1 to 4 generally handle network control and data transmission and reception. Layers 5 to 7 handle application issues. Specific functions of each layer may vary depending on factors such as protocol and interface requirements or specifications that are necessary for implementation of a particular layer. For example, the Ethernet protocol may provide collision detection and carrier sensing in the data link layer. Layer 1, the physical layer, is responsible for handling all electrical, optical, opto-electrical and mechanical requirements for interfacing to the communication media. Notably, the physical layer may facilitate the transfer of electrical signals representing an information bitstream. The physical layer may also provide services such as, encoding, decoding, synchronization, clock data recovery, and transmission and reception of bit streams. In high bandwidth applications having transmission speeds of the order of Gigabits, high-speed electrical, optical and/or electro-optical transceivers may be used to implement this layer.
As the demand for higher data rates and bandwidth continues to increase, equipment capable of handling transmission rates of the order of 10 Gigabits and higher is being developed for high-speed network applications. Accordingly, there is a need to develop a 10 Gigabit physical layer device that may facilitate such high-speed serial data applications. For example, XENPAK multi-source agreement (MSA) defines a fiber optical module that conforms to the well-known IEEE standard for 10 Gigabit Ethernet (GbE) physical media dependent (PMD) types. In this regard, XENPAK compatible transceivers may be used to implement the physical layer. Notwithstanding, there is a need for transceivers, which are necessary for implementing 10 Gigabit physical layer applications. The well-known IEEE P802.3ae draft 5 specifications describes the physical layer requirements for 10 Gigabit Ethernet applications and is incorporated herein by reference in its entirety.
An optical-based transceiver, for example, may include various functional components which may implement tasks such as clock data recovery, clock multiplication, serialization/ de-serialization, encoding/decoding, electrical/optical conversion, descrambling, media access control (MAC), controlling, and data storage. These functional components may be implemented in a separate chip and/or integrated circuit (IC).
The proliferation of physical layer devices designed to provide high speed communication services will undoubtedly give rise to the need for testing the reliability of any communication links in which these physical layer devices are employed. The testing of communications links may often involve the application of one or more test signals to the inputs of the communication links and capturing the output signals by an external device. The external device may typically store and compare the captured outputs against expected outputs that are known to be accurate. In this regard, defective links or devices comprising the links may be detected when the captured output signals are inconsistent with the expected outputs.
One parameter that may be used to evaluate the reliability of a high speed communication link is bit error rate, which may also be called the bit error ratio (BER). The BER may be defined as a number of erroneous bits divided by the total number of bits transmitted, received, or processed over some stipulated period. When dealing with information, BER may be defined to be the number of erroneous decoded (corrected) bits divided by the total number of decoded (corrected) bits. The BER may usually be expressed as a coefficient and a power of 10. For example, 2.5 erroneous bits out of 100,000 bits transmitted may be represented as 2.5 out of 105 or 2.5×10−5.
Testing BER for a communication link by applying input signals and capturing of outputs by an external device may become difficult as the data rate of the communication links increase. To effectively simulate operational conditions, the external device must apply the input signals and capture the outputs at the operational data rate of the chip. Testing optical transceivers may be challenging because of the high speeds at which these devices operate. Accordingly, a need exists for achieving BER testing for a physical layer multimode device that may operate at speeds of the order of about 10 Gbps.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.